Sep 24, 2014 - MICROFOSSIL RECORD AND FACIES TRANSITIONS OF OXFORDIAN TO BERRIASIAN. CARBONATES IN THE WESTERN SREDNOGORIE, ...
Bul. Shk. Gjeol. 2014 - Special Issue Proceedings of XX CBGA Congress, Tirana, Albania, 24-26 September 2014
Special Session
Buletini i Shkencave Gjeologjike
Proceedings XX Congress of the Ca r pat h i a n - Ba l k a n Geological Association September 24-26, 2014 Tirana Albania
Editors
Special Issue Volume 2/2014 General Sessions
Beqiraj A. Ionescu C. Christofides G. Uta A. Beqiraj Goga E. Marku S.
tirana 2014 tirane 2014
Bul. Shk. Gjeol. 2/2014 - Special Issue Proceedings of XX CBGA Congress, Tirana, Albania, 24-26 September 2014
General Session G02
Microfossil record and facies transitions of Oxfordian to Berriasian carbonates in the Western Srednogorie, Bulgaria Petrova S1, Ivanova D1, Nikolov N1, Koleva-Rekalova E1 and Lakova I1 Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str. Bl. 24, 1113 Sofia, Bulgaria, silviya_p@geology. bas.bg
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Abstract
Formation is determined as Oxfordian based on the record of the calcareous dinocysts Colomisphaera fibrata and Colomisphaera pieniniensis. Upwards, the mainly grained and lithoclastic limestones of the Glozhene-Slivnitsa Formation are determited as Late Tithonian based on the calpionellid Boneti Subzone, Praetintinnopsella Zone and Remanei Subzone, as well as on the first occurrence of the foraminiferal species Protopeneroplis ultragranulata. Microincrusting foraminifera that are typical of the carbonate platform were redeposited in the Glozhene-Slivnitsa Formation.
The study area attracted the present authors’ interest for the following reasons: complex relationships and fast facies transitions between Upper Jurassic and Berriasian carbonates of three distinct depositional settings (carbonate platform, pelagic basin and flysch trough); scarcity so far of abundant paleontological data on strata, except the Kimmeridgian; new results from the recent 1:50000 geological mapping. This work presents the description of five, Oxfordian to Berriasian carbonate sections, in the Western Srednogorie; the calpionellid, foraminiferal and calcareous dinocyst distribution and precise dating and facies transitions. Subject of this study are the Yavoters, Gintsi, Glozhene, Slivnitsa, Salash-Cherni Osam, and Cherni Osam Formations, their vertical and lateral passing, age determination, carbonate microfacies and evolution of the depositional environment.
Dragovishtitsa West section. The Yavorets Formation is assigned to the interval from Middle Callovian to Oxfordian based on the recorded calcareous dinocysts and the foraminiferal Ophthalmidium strumosum Zone. The age of the clayey nodular limestones of the Gintsi Formation is determined as Late Kimmeridgian and Early Tithonian on the record of the calcareous dinocysts Colomisphaera nagyi, Stomiosphaera moluccana, and Parastomiosphaera malmica. The Gintsi Formation is covered with a considerable stratigraphical hiatus by the Early but not earliest Berriasian Glozhene-Slivnitsa Formation (Elliptica Subzone). The abundant foraminiferal Coscinoconus assemblage had allochthonous character in the Glozhene Formation since normally it occurs in the shallow-water subtidal zone.
Dragovishtitsa 1 section. The Chitinoidella Zone (Dobeni and Boneti subzones) corresponds to the upper part of Gintsi Formation and the basal 3 m of the Glozhene Formation. The Praetintinnopsella Zone is represented only by its index species in the lower part of Glozhene Formation. Elliptica Subzone in this section corresponds to a 2 mthick interval of transitional sediments between the Glozhene and Slivnitsa formations, in both macroscopic features and microfossil content.
Dragovistitsa East section. The Cherni Osam Formation here represents a pre-flysch triple alternation of sandstones, clayey limestones and micritic limestones and is of Early Berriasian age (Alpina, Remaniella and Elliptica subzones). This evidences an Early Berriasian onset of the carbonate turbiditic deposition in the area.
Dragovishtitsa 2 section. The Salash-Cherni Osam Formation represents alternation of clayey limestones and limy sandstones. The whole section corresponds to the Elliptica Subzone. The ammonites found are Berriasella (B.) cf. vranensis and Jabronella (J.) cf. fuelopi. The former species was only reported from its type locality in the Upper Berriasian. The co-occurrence of Berriasella (B.) cf. vranensis with calpionellid associations of Elliptica Subzone indicates its lower stratigraphic range.
Stratigraphic hiatuses. The Upper Tithonian Chitinoidella and Praetintinnopsella Zones and the Berriasian Elliptica Subzone of Calpionella Zone are documented in Dragovishtitsa 1 section. It is noteworthy that the Uppermost Tithonian Crassicollaria Zone and the Lower Berriasian Alpina and Remaniella subzones are absent. In
Dragovishtitsa South section. The age of the micritic and grained limestones of the Slivnitsa 79
Bul. Shk. Gjeol. 2/2014 - Special Issue Proceedings of XX CBGA Congress, Tirana, Albania, 24-26 September 2014
General Session G02
debris from the carbonate platform and the shelf edge. It differs from the typical development in the distal pelagic basinal parts of the West Balkan Mts and is here designated as the “Glozhene-Slivnitsa Formation”. From NW to SE, the biogenic carbonate platform limestones of tSlivnitsa Formation pass to the pelagic limestones of the Yavorets, Gintsi, Glozhene-Slivnitsa and SalashCherni Osam Formations, and further to SE – to the carbonate turbidities of the Cherni Osam Formation.
Dragovishtitsa West section parts of the Tithonian and Berriasian are missing. In Dragovishtitsa South section the stratigraphic hiatus corresponds to the Kimmeridgian and the Early Tithonian. These results differ significantly from all Oxfordian to Berriasian pelagic sections in the Western Balkan and Western Fore-Balkan in Bulgaria where the sedimentary record is continuous. Facies transitions. The Glozhene Formation, even rich enough in chitinoidellids and calpionellids, contains also allochthonous foraminifera and
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